Biological culture is an important bioprocess for cell growth. The growth curve of cells can demonstrate the effect of environmental chemicals, pH, temperature, and other parameters and endogenous factors on the corresponding cells. Here the biological cells include microorganism cells (bacteria, yeast, or fungi), human cells, animal cells and insect cells. Real-time and on-line monitoring a biological cell culture, especially in a dynamic environment such as an incubator/shaker, is quite valuable in a variety of fields including biotechnology, pharmaceutics, clinical medicine, agriculture and food industry.
Existing biological cell culture equipments range from simple incubators, incubated shakers, or shakers to sophisticated and expensive bioreactors. Among them, the incubator/shakers for small to medium volume (<5000 ml) biological culture containers like culture flasks are the most widely used equipments in laboratories. Here the incubator/shakers is a term for incubated shakers or shakers. These incubated/shakers have shaking platforms which can move horizontally with an orbital circle. This conventional cell culture method has been used for many many years. However, so far, there is no a real-time and on-line culture monitoring system being developed for detecting the growth curve or concentration of biological cell culture with such small to medium volume culture equipments.
The concentration of biological cells is one of direct indicators for the biological culture status, apart from pH, dissolved oxygen and dissolved carbon dioxide. The two most common techniques of measuring the concentration of the cells are spectrophotometery and hemocytometry. The spectrophotometer technique is to detect the turbidity of biological culture media in term of optical density (OD) and the hemocytometer technique is to count the biological substance number in a diluted biological medium.
The principle of spectrophotometer is that the intensity of the light which is transmitted through a biological medium containing an absorbing and scattering substance like cells and proteins is decreased by that fraction which is absorbed and scattered, and this fraction can be detected and measured photo-electrically.
Generally, there are two kinds of concentration measurement using the spectrophotometery method for biological cell culture. First one is to utilize a special cuvette or a test tube with a small volume (about 1 ml). To perform such conventional measurement for a growing biological substance like microorganisms in a flask, it usually requires withdrawing a small sample from the biological medium and putting the sample in a cuvette or a test tube for a spectrophotometer measurement. This kind of measurement is discrete and can cause a disruption for biologic culture. The second is to utilize a stick-shape probe with a light emitter and a light sensor or optical fibers. This kind of spectrophotometer is usually designed for bioreactors. Although this kind of device can perform continuous measurement, it is still very difficult for this kind of spectrophotometers to operate in a shaking environment. The measurement requires submerging the probe in a biological medium and sterilization is always required.
These existing measurements become very tedious and even impossible when a real-time and on-line continuous concentration measurement is required especially when biological cells are in growing and shaking environment. A real-time, on-line and automatic measurement of biological cell growth curve, concentration or even other properties such as pH and CO2 in an incubator/shaker culture environment will allow culture process to be very efficient and productive and can solve logistic problems and save time and efforts for users.